![]() Rays have a comparatively large, oily liver that helps maintain their buoyancy as oil is positively buoyant in water. This means that when a ray stops swimming it will sink toward the sea floor unless the animal is buoyed up by a current or upwelling. The swim bladder is used to help control the buoyancy as well as ascent and decent rates in bony fishes. The bodies of numerous species are coated with a slimelike mucous that reduces friction, or drag, as the rays swim, thus increasing their efficiency and swimming speed.Īs is the case with sharks, rays lack the internal organ known as a swim, or gas, bladder that is found in many bony fishes. Many species of rays can swim fast enough that they can “jump” above the surface, providing a momentary thrill for onlookers. Their enlarged pectoral fins also help enable rays to glide through the water column without sinking too rapidly. ![]() Rays propel themselves with their powerful, winglike pectoral fins that undulate, or ripple, in some species and that beat like more semirigid wings in others. The skin of rays is composed of modified scales known as dermal denticles (also known as placoid scales) that look like “miniature teeth.” Rays possess five to seven pairs of slitlike gill openings on each side of the head along the underside of the body. The pectoral fins are connected to the rest of the body and together the body and pectorals form the “disc.” The tails of rays also vary from the short, stubby tail of some electric rays to the more than 10-foot- (3-m-) long whiplike tails of some stingrays. Having been greatly modified over the eons, their pectoral fins are relatively large. On the whole, the bodies of rays have a generally flattened shape and an elongated tail. Some rays are commonly found very close to the shoreline while other species live in the extreme depths of the sea down to 10,000 feet (3,000 m). Many species live on or near the sea floor while others live in the water column and are adapted for continuous swimming. Modern rays inhabit oceans, seas, bays and estuaries around the world. Because rays lack bones, fossil remains are extremely rare, however, their teeth are composed of very hard enamel, and they are prone to fossilization. The earliest rays are thought to have appeared on Earth about 150 million years ago during the Jurassic period. Rays are believed to have evolved from sharks. So, while the vast majority of fishes have bony skeletons and are described in the class Osteichthyes, rays, sharks, skates and ratfishes possess skeletons made of cartilage, and are described in the class Chondrichthyes. Rays are fishes whose skeletons are composed of cartilage, not bone. It might surprise you to read that rays are fishes, but this is no misprint. They, of course, are rays, a diverse group of about 500 species of fishes that are a welcome sight on any dive. The bodies of some are protected by numerous “thornlike spikes,” while the bodies of many others appear relatively smooth. Some species have long whiplike tails, and others very short tails. Some weigh more than 2 tons while others can fit into the palm of your hand. Others have no barb at all, and still others possess the ability to deliver a potent electric shock. Some have potent spines, or “stingers” on their tails. Some appear to “fly” with extraordinary grace while still others undulate their fins to propel themselves. Others rest out in the open on the sea floor and are relatively easy to spot. Some bury themselves so well in sand bottoms that all you see is a faint outline of their bodies.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |